x86/tdx: Fix typo in comment in __tdx_hypercall()

Comment in __tdx_hypercall() points that RAX==0 indicates TDVMCALL
failure which is opposite of the truth: RAX==0 is success.

Fix the comment. No functional changes.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/all/20230126221159.8635-2-kirill.shutemov%40linux.intel.com

arch/x86/coco/tdx/tdcall.S

@@ -155,7 +155,7 @@ SYM_FUNC_START(__tdx_hypercall)
 	tdcall
 
 	/*
-	 * RAX==0 indicates a failure of the TDVMCALL mechanism itself and that
+	 * RAX!=0 indicates a failure of the TDVMCALL mechanism itself and that
 	 * something has gone horribly wrong with the TDX module.
 	 *
 	 * The return status of the hypercall operation is in a separate